The increasing demand for water among households, industry, the environment, and especially agriculture is making global water scarcity a perilous possibility. However, salt or brackish water is readily available in many areas of the world. In fact, 97 percent of the surface water of the earth is salt water.
Much of the projected increase in water demand will occur in developing countries, where population growth and industrial and agricultural expansion will be greatest. The world's thirst for water is likely to become one of the most pressing resource issues of the 21st Century.
One-quarter of the world's population lives in areas where water is physically scarce, while about one-sixth of humanity—over a billion people—live where water is economically scarce. Declining groundwater supplies, pollution, flooding and drought could well worsen poverty in many areas.
Irrigation already accounts for about two thirds of water use worldwide. As rivers and lakes are dammed, dried up, or polluted, and as food demand grows in the next 50 years, farmers will become increasingly dependent on ground water for irrigation.
Nearly one third of all humanity relies almost exclusively on groundwater for drinking, including the residents of some of the largest cities in the developing world. Today water tables are falling on every continent. The depletion of aquifers is a new problem, one that has emerged only in the half past century or so, because it is only in this period that we have had the pumping capacity to quite literally deplete aquifers.
Desalination of sea water has been practiced for over half a century and is a well known means of water supply in many countries.
Evaporation and reverse osmosis are two common methods to produce fresh water from sea water. Evaporation methods involve heating the sea water, condensing the vapor produced and isolating the distillate.
Reverse osmosis is a membrane separation process in which the water from a pressurized saline solution is separated from the dissolved material by flowing through a membrane.
In U.S. Pat. No. 3,456,802, osmotic membranes units are submerged at great depths in the sea, 3,000 to 4,000 feet, to take advantage of the hydrostatic pressure of the ocean for supplying the necessary differential pressure to the osmotic membranes.
U.S. Pat. No. 4,125,463 discloses a reverse osmosis apparatus placed in a well hole and using the head pressure of the salt water to supply the necessary differential pressure to the osmotic membranes.
In U.S. Pat. No. 5,229,005, a reverse osmosis apparatus is lowered into the ocean by means of lines attached to pulleys, then raised to the surface to remove the fresh water produced. The invention also uses hydrostatic pressure of the ocean for supplying the necessary differential pressure to the osmotic membranes.
U.S. Pat. No. 6,800,201 discloses a large open top metal cylinder anchored to the sea floor with several units of osmotic membranes attached to the side of the cylinder. Due to the pressure differential, freshwater passes through the membranes by reverse osmosis. The brine is disposed back to the ocean by gravity through an opening in the bottom of the cylinder.
Energy costs for desalination of prior inventions is still high, and one of the main drawbacks to the use of reverse osmosis systems as used by the prior art is the pumping energy required for raising the sea water to the pressures necessary for osmotic separation. These pressures are typically in the neighborhood of 800 to 1000 psi. The problem is amplified by the increasing cost of energy and the ongoing decreasing supply of available energy resources.
The above cited prior art inventions have attempted to save pumping energy by using the hydrostatic pressure of the ocean to desalinate seawater by reverse osmosis, but none of them have proved to be practical or economically viable since they all require the invention to be placed at great depths above 3,000 feet in order to obtain the required pressure of 800 to 1000 psi for osmotic separation. The amount of energy saved by such a process is offset by installation and maintenance costs since it requires working in extremely deep waters. Furthermore the important head requires substantial energy to pump the fresh water to the surface.
The present invention is distinguishable from the above prior art in that it can be located at much lower depth, as low as 70 feet. It combines the use of the ocean hydrostatic pressure and the sea currents renewable energy to supply the necessary differential pressure to the osmotic membranes.
It is an object of the present invention to reduce the pumping energy required for the desalination process.
Another object of this invention is the use of renewable energy for the three following pumping processes, contributing to the protection of our environment: pumping to raise the feed water pressure to reverse osmosis operational pressure above 800 PSI, pumping the brine back to the ocean, and pumping the product water to an onshore storage tank and the distribution network.
Another object of this invention is to eliminate the feed water and pre-filtration pumping processes by using exclusively the hydrostatic pressure of the ocean.
Another object of this invention is the discontinued use of land and building facilities for the desalination process. Land leasing, construction and contractor costs can therefore be avoided, reducing substantially the initial capital costs of the project. Only the product water storage will be required onshore.
Another object of this invention is to keep the desalination system unseen from shore, avoiding obnoxious noise and visual impact on the shoreline. Therefore, this invention is submerged at a sufficient depth to allow free maritime traffic over the operating area.
Another object of this invention is to facilitate an increased amount of output of desalinated water without the need to upgrade existing equipment. The vessels of this invention are stand alone and turnkey units, providing a modular plant design that can be easily upgraded and modified. The expansion of present facilities is only limited by the offshore operating area granted by the local authorities.
Another object of this invention is to reduce maintenance and installation cost issues by placing the invention into shallow waters less than 1200 feet, and regular maintenance is possible from the surface without the requirement of divers or submersible maintenance equipment to work on, repair, or maintain the system.
Another object of this invention is to provide the means to be rapidly moved to an alternate location in order to optimize the use of renewable energy resources and/or relocate the location of a source of intake water and the discharge of brine.
Another object of this invention is to produce large quantities of fresh water in locations distant from any public water distribution network or grid power source.
Another object of this invention is to reduce the accumulation of concentrated brine released by conventional desalination plants. Conventional desalination plants release their brine through pipelines laid on the seabed a few miles from shore. In absence of sufficient currents or water mixing at the disposal spot, the accumulation of concentrated brine could be harmful for the sea flora and fauna. This invention is designed to release the brine in the middle of strong sea currents at mid-depth, thus providing a rapid dispersion with minimal impact on the environment.
Another object of this invention is to reduce the risk of sea life impingement through the feed water intake system. Conventional desalination plants use single spot intake systems with particularly strong suction flows, while the modular configuration of this invention allows an efficient dispersion of the suction effect, as the desalination vessels are kept at a specific distance from each other.
Additional features of this invention will be apparent with the following description and accompanying drawings.